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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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16th Oct 2017, 8:46 pm | #1 |
Heptode
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Location: Ellesmere, Shropshire, UK & Co. Cork, Ireland.
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RGD tabletop radiogram
My daughter is showing an interest in this set lingering in the attic which means next in line in the roundtoit queue to be reactivated! I can't seem to identify it as the base is missing and no model numbers or badges can be found on the case. The chassis seems to have a 5 valve plus U50 rectifier line up with possibly a pair of output valves (push/pull)? It's not a radio, nor is it a record player and it's not a radiogram. What is it called? A tabletop radiogram?
The record deck is a Collaro. The set was given to me from a neighbour whose parents probably owned it from new and it is heavy! I will get some pictures of the chassis soon.
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Dom Less snakes...more ladders! |
16th Oct 2017, 9:08 pm | #2 |
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Re: RGD tabletop radiogram
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23rd Oct 2017, 7:16 pm | #3 |
Heptode
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Re: RGD tabletop radiogram
Thanks Lawrence!
Earlier today I extracted the chassis after wrestling with a jammed knob which eventually gave up with no damage. This set looks to be well used with some mischief going on with insulation tape and some dodgy looking soldering (or maybe wire wrapping) on the volume or tone pot. The valves all have their getters. The mains TX is big and chunky and the output TX is also generously sized. Next is some basic checks for shorts etc. and an on sight replacement of a blackened wax cap below the EL84s. I see blobs of red quality control paint on nearly all the soldering which should show up what work has gone on.
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Dom Less snakes...more ladders! Last edited by sexton_mallard; 23rd Oct 2017 at 7:22 pm. Reason: Added comment about quality control paint on soldering. |
31st Oct 2017, 10:46 pm | #4 |
Heptode
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Location: Ellesmere, Shropshire, UK & Co. Cork, Ireland.
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Re: RGD tabletop radiogram
On applying power, with increasing lamp limiter bulb wattages, the chassis came to life with stations on MW SW and very weak on LW. HT then fell away and dropped to under 80VDC. I swapped the U50 rectifier with a 5Z4G borrowed out of a McMichael 481 in the roundtoit queue. This did the trick with about 260VDC now showing, The mains 32+32mfd smoothing can remains nice and cool. Measuring 16v and 19v dc on the grids of the two EL84s . Time for some more new capacitors.
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19th Nov 2017, 5:16 pm | #5 |
Heptode
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Re: RGD tabletop radiogram
All wax caps have now been replaced. Volume is now good and sensitivity is good on all wavebands. The only niggle so far is a mains hum which gets a bit louder after about 20 minutes of running. All valves apart from the rectifier have been substituted from other sets that are working fine to rule out any heater-cathode faults. All original valves are back in the set (apart from the replacement rectifier which is good).
The ECH81 was in better condition in this set than the one borrowed from a working set! I'm seeing 240-260v DC on both sections of the smoothing can but about 3-4v AC on one section and less than 1v AC on the other. Could this be the ripple on the section that has possibly dried out? Time to order in some more mains electrolytics. I will check the coax wiring again in the meantime as this looks to have been fiddled with and could also be a source of hum.
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Dom Less snakes...more ladders! Last edited by sexton_mallard; 19th Nov 2017 at 5:21 pm. |
9th Dec 2017, 10:35 am | #6 |
Heptode
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Re: RGD tabletop radiogram
After a bit of prodding around and checking of resistor values (all of which are a little high but only 10-15%) I eliminated the hum. Because the base cover is missing, a lot of the components were pushed up into the chassis as the base of the chassis is exposed. A noisy resistor in the ECC83 area went quiet once pulled back out,and some reflowing of some dry looking connections in the amp section did the trick. The volume pot was opened and give a flush of Servisol. 'Big Bertha' as it is now known has a lot of black dust possibly soot which is greasy either combined with nicotine or it is soot from diesel as the owners family were/are truckers and truck mechanics. The grime on the knobs certainly suggest it may have spent time as a workshop radio?
Bertha was promoted to last weekend's in house entertainment system while the Christmas deccies went up, playing on MW and from a tablet streaming web radio on the gram socket. I found that the twin speakers were out of phase and reversing the connections on one speaker sorted it. This appears to have left the factory like this? One of the dial bulbs was a 12v type. This was changed for a 6.3v bulb. Attention turned to the collaro deck which will take a couple of rounds of cleaning. The idler wheels are ok but the autochanger driver has insulating tape already added. The main platter bush and bearing is well lubricated adding some credence to the workshop use theory. The chinese ceramic cartridge arrived. Attached are some snaps of the cartridge showing the size comparison and a close up of the stylus and cantilever. Not bad for a couple of quid. I will test the original cartridge first which will need a new stylus, it will not probably see use as I want to play stereo records.
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Dom Less snakes...more ladders! Last edited by sexton_mallard; 9th Dec 2017 at 10:58 am. |
9th Dec 2017, 10:41 am | #7 |
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Re: RGD tabletop radiogram
I've found those red and black cartridges to be great for the money, where else can you buy a stereo cartridge with stylus for less than £2 delivered?
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9th Dec 2017, 11:10 am | #8 |
Dekatron
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Re: RGD tabletop radiogram
The yellow BSR cartridge that is fitted at the moment is fine for stereo records. It's one of the "stereo compatible" versions, which means that is has the necessary vertical compliance to play stereo records without harm.
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9th Dec 2017, 11:23 am | #9 | |
Octode
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Re: RGD tabletop radiogram
Quote:
Steve |
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9th Dec 2017, 12:19 pm | #10 |
Dekatron
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Re: RGD tabletop radiogram
BTW that Yellow BSR stereo-compatible cartridge is a (by now a very rare) high-output type and, if still working to original spec, may need careful matching to the ampilfier.
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Edward. |
9th Dec 2017, 9:06 pm | #11 | |
Heptode
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Re: RGD tabletop radiogram
Quote:
I forgot to add earlier that one of the speakers were holed in 2 places. I cut the card cone out of a scrap PC speaker and patched over the holes using a bit of PVA. The difference it made was amazing. I have bought one of those Chinese made MP3/FM/Bluetooth modules to add in due course but more on that later.
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10th Dec 2017, 11:56 am | #12 |
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Re: RGD tabletop radiogram
The plastic cantilever on the ST9 stylus is of a lower compliance than the metal cantilevered versions e.g. the ST12. They tended to be used more on high-output cartridges.
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Edward. |
31st Dec 2017, 1:30 am | #13 |
Heptode
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Re: RGD tabletop radiogram
The new stylus arrived which appears to be new production in black plastic with LP and LP (diamond symbol) sides. This fitted easily in the original cartridge. I cleaned the platter bearing and bushes with carburettor cleaner and applied grease to the ball bearing and 3 in 1 to the bushes sparingly around the works of the autochanger. The motor bush carrier was removed and the top and bottom motor bushes oiled liberally. The deck was then left to rest for a few days on an old newspaper to let excess oil to drip off. Tonight I decided to give it a run and lashed up the deck to a temporary power supply and reconnected to the gram socket on the radiogram chassis.
The cartridge is good . Playback is reasonable if a little light on bass but treble is good and with no noticeable wow and flutter with plenty of volume. The autochanger is a bit erratic, sometimes cancelling itself and placing the tonearm at the 10 inch edge with a LP but I will go through and do some fettling after re-reading some of the excellent stickies under this forum heading. Big Bertha might get promoted to some New Year's Eve entertainment services at this rate!
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31st Dec 2017, 3:59 pm | #14 |
Dekatron
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Re: RGD tabletop radiogram
You may need to look at the actuation of the sizing spigot in the column, when a 12" LP drops it should fully retract back into the column. I note the overarm finger lift is now fitted onto the tone arm. A good idea - I did this on my RC456. It only slightly adds to the tone arm weight.
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Edward. |
31st Dec 2017, 7:07 pm | #15 |
Heptode
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Re: RGD tabletop radiogram
Thanks Edward, I will check. With more playing it is apparent the treble is very cut off, what I was hearing as treble was 'needle talk' coming from the tonearm. I realise that I will not get Hi Fi quality sound but medium wave starts to sound like FM in comparison. I take it that this cartridge (a BSR X3M?) is a retrofit and the original cartridge was a double sided flip-over model, hence the cutout in the headshell for the lever. The stylus has two respectable looking diamonds (see pic), one of which I expected to be a larger size for 78s but I understand this stylus is double LP/microgroove with a synthetic sapphire and a diamond. Looking at the tonearm on the record, the stylus looks to be about 30-40 degrees from the vertical (see pic) which may explain the lack of treble but I suspect this frequency response could be a feature of a aged crystal cartridge. The cartridge is set at a 20 degree slant in the headshell. Is this intended or should it be set more parallel? I measured the tracking weight - 14g! is this about right? Also, after playing some sacrificial charity shop records, I can see where I have played on the record!
I will remove the cartridge from the headshell to check this and will try setting the cartridge flatter.
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31st Dec 2017, 7:35 pm | #16 | |
Dekatron
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Re: RGD tabletop radiogram
Quote:
Whoa!! 14 grams is way over the top. No wonder you can see where the record has been played, the stylus is grinding the grooves to dust. Around 5-6 grams is about right. |
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31st Dec 2017, 9:53 pm | #17 |
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Re: RGD tabletop radiogram
I've been through the "daughter taking an interest in various items" experience Dom. It's a retro world now
Your restoration has gone well, just the tracking weight to "finess". There are a lot of positive comments about the [medium output] chinese ceramic cartriges [p*/7*] on the Forum. I keep meaning to ask if there is a particular supplier of these handy items that is recommended? Cheers and a Happy New Year Folks! |
31st Dec 2017, 10:06 pm | #18 |
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Re: RGD tabletop radiogram
The cartrigde should be at -15 degress rearwards from the vertical. The tracking weight should be no more than 4-5 grams.
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Edward. |
1st Jan 2018, 12:41 am | #19 |
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Re: RGD tabletop radiogram
Further to my enquiry, I see that Paul Sherwin has just answered a similar request on the AG79 thread so no need to respond further unless there is a specific point to make.
Thanks, Dave W |
1st Jan 2018, 1:18 am | #20 |
Heptode
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Re: RGD tabletop radiogram
Thanks Edward. I checked the accuracy of my digital scales using coins and removed the cartridge from the headshell. The tonearm weighs 10g, the cartridge + white plastic mounting + screw is about 4g. I can't see any provision on the tonearm for adjusting tracking weight nor can I easily see a way of mounting a counterweight to the 'elbow' of the tonearm. The long spring is slack when the arm is in the playing position and is applying no additional downforce
The cartridge went dead when removed and was silent when I remounted. I tapped the headshell gently a few times and the cartridge came back to life . Here is a picture of the underside. The black item midway is a soft rubbery plug possibly for vibration damping with negligible mass. I'd be interested to know what the tracking weights of other similar Collaro decks out there are.
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Dom Less snakes...more ladders! Last edited by sexton_mallard; 1st Jan 2018 at 1:31 am. |